It is obvious that one valave is leaking..I find it hard to believe that a builder would have put a valve under ground without having access to it. A valve will fail sometime along the way, no valve is going to last forever. However, you never know what a builder will do during construction...It doesn't take a whole lot for a valve to fail, usually it is a crack in the housing or a "o" ring failure. I would try to talk to the builder if at all possible prior to ripping up any concrete deck...Maybe have the service company do a pressure test to try to isolate what might be leaking to allow the upper bodies of water to drain down as they have.
I would still look at the above ground system for a crack or "o" ring failure ..double check anything that has "o" rings or gaskets.